Effect of immobilization of titanocene catalyst in aralkyl imidazolium chloroaluminate media on performance of biphasic ethylene polymerization and polyethylene properties

1-(2-Phenylethyl)-3-methylimidazolium and 1-benzyl-3-methylimidazolium chloroaluminates, [Ph-C₂mim][AlCl₄] and [Bzlmim][AlCl₄], were applied as media of the Cp₂TiCl₂ catalyst for biphasic ethylene polymerization. The studied aralkyl ionic liquids ensure greater stability of the catalyst at higher temperatures and more regular morphology of the produced polyethylene than analogous 1-n-alkyl-3-methylimidazolium chloroaluminates. The alkylaluminium compound participates in the termination reaction of the polymer chain. The catalyst is stable and enables recycling of the ionic liquid phase in the consecutive polymerization reactions. The [Ph-C₂mim][AlCl₄] ionic liquid and AlEt₂Cl alkylaluminium compound turned out to be the most suitable for the biphasic process. The influence of the kind of ionic liquid, alkylaluminium compound (AlEt₂Cl and AlEtCl₂), activator/catalyst molar ratio, reaction temperature, reaction time and catalyst recycling on the polymerization performance as well as polyethylene properties such as molecular weight (M _w ), polydispersity, melting temperature, crystallinity degree, bulk density and particle size is presented.     

Heterogeneous Enantioselective Synthesis of a Dihydropyran Using Cu-Exchanged Microporous and Mesoporous Materials Modified by Bis(oxazoline)

The formation of dihydropyran from the Diels–Alder reaction between E-ethyl-2-oxo-3-pentenonate and vinyl ethyl ether is investigated using copper (II) bis(oxazoline) as catalyst. The homogeneously and heterogeneously catalyzed reactions are contrasted. Immobilization using mesoporous materials (Cu-MCM-41, Cu-AlSBA-15, Cu-MSU-2) and zeolite Y is found to produce an effective heterogeneous catalyst. Although the level of enantioselection is not high in this initial study, the CuH-zeolite Y/bis(oxazoline) catalyst gives the highest ee (41% ee), which is significantly higher than that observed for the Cu(OTf)₂ homogeneous catalyst (20% ee) under comparable conditions. In addition, with the heterogeneously catalyzed reaction, the enantioselection changes from the initial 2R,4S product to the 2S,4R diastereoisomer. This behavior is not observed with the homogeneously catalyzed reaction, which always yields the 2R,4S product. These results are discussed in terms of the confinement of the catalyst complex within the pores of the heterogeneous catalyst.     

Preparation of exfoliated isotactic polypropylene/alkyl-triphenylphosphonium-modified montmorillonite nanocomposites via in situ intercalative polymerization

Alkyltriphenylphosphonium-modified montmorillonite(PMMT) was used to prepare TiCl₄/MgCl₂/PMMT compound catalyst and exfoliated i-PP/PMMT nanocomposites were prepared by in situ intercalative polymerization of propylene with TiCl₄/MgCl₂/PMMT catalyst. The catalytic efficiency of the above catalyst under optimum polymerization condition could reach as high as 1300 kg/(molTi h) and the combining of PMMT with Z-N catalyst do not change the stereo-regulation catalytic properties of the Z-N catalyst. The synthesized PP possessed high isotacticity, melting point and molecular weight. Wide angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) examinations evidenced the nanocomposites obtained were exfoliated ones.     

Microwave catalytic NOx and SO2 removal using FeCu/zeolite as catalyst

Non-thermal plasma technology is a promising process for flue gas treatment. Microwave catalytic NO_x and SO₂ removal simultaneously has been investigated using FeCu/zeolite as catalyst. The experimental results showed that a microwave reactor with FeCu/zeolite only could be used to microwave catalytic oxidative 91.7% NO_x to nitrates and 79.6% SO₂ to sulfate; the reaction efficiencies of microwave catalytic reduction of NO_x and SO₂ in a microwave reactor with FeCu/zeolite and ammonium bicarbonate (NH₄HCO₃) as a reducing agent could be up to 95.8% and 93.4% respectively. Microwave irradiation accentuates catalytic reduction of SO₂ and NO_x treatment, and microwave addition can increases SO₂ removal efficiency from 14.5% to 18.7%, and NO_x removal efficiency from 13.4% to 18.7%, separately. FeCu/zeolite catalyst was characterized by X-ray diffraction (XRD), X-ray photoelectron spectrum analysis (XPS), scanning electron microscopy (SEM) and the Brunauer Emmett Teller (BET) method. Microwave catalytic NO_x and SO₂ removal follows Langmuir-Hinshelwood (L-H) kinetics.     

Effect of polymerization conditions on the polymer properties of CO2-cyclohexene oxide copolymer prepared by double metal cyanide catalyst

The effect of polymerization parameters such as polymerization time, temperature, pressure and the amount of catalyst amount in CO₂-cyclohexene copolymerizations with double metal cyanide (DMC) catalyst were investigated in detail. Especially, the effect of polymerization conditions on the polydispersity index (PDI) and glass transition temperature (T_g) were deeply examined. Increases in polymerization time, pressure, temperature and the amount of catalyst in feed increased the activity of the DMC catalyst. The molecular weight (MW), PDI and glass transition temperature (T_g) were affected by the polymerization time, temperature, pressure and the amount of catalyst in the feed.     

Kinetics of Selective Oxidation of Dimethyl Ether to Formaldehyde Over Al2O3-Supported VO x and MoO x Catalysts

The object of this work is to study the effect of hydrothermal treatment on the TS-1/SiO₂ catalyst in propylene epoxidation in fixed bed. The TS-1/SiO₂ catalysts before and after hydrothermal treatment were characterized by means of XRD, XRF, BET, UV–Vis and EPR techniques. It was found by EPR characterization that two types of Ti(IV)-superoxide radicals, A (g _z = 2.0271; g _y = 2.0074; g _x = 2.0010) and B (g _z = 2.0247; g _y = 2.0074; g _x = 2.0010), were observed for the TS-1/SiO₂ catalyst. The superoxo species A was converted to B after the TS-1/SiO₂ catalyst was hydrothermally treated. The results show that hydrothermal treatment temperature and time have marked effects on the activity and the PO selectivity. The optimal hydrothermal treatment temperature and time are 170 and 4 h, respectively. In the long-term propylene epoxidation reaction, about 95% H₂O₂ conversion and above 94% PO selectivity are obtained over TS-1/SiO₂ catalyst hydrothermally treated at 170° C for 4 h.     

Effect of an Ionic Liquid on the Catalytic Performance of Thiocyanatodioxomolybdenum(VI) Complexes for the Oxidation of Cyclooctene and Benzyl Alcohol

The complexes (PPh₄)₂[Mo^VIO₂(NCS)₄] (1), Mo^VIO₂(NCS)₂(di-tBu-bipy) (2) and Mo ₂ ^VI O₅(NCS)₂(di-tBu-bipy)₂ (3) (di-tBu-bipy = 4,4′-di-tert-butyl-2,2′-bipyridine) were studied as catalyst precursors for the oxidation of cyclooctene (Cy8) and benzyl alcohol (BzOH), using either dimethyl sulfoxide (DMSO) or tert-butyl hydroperoxide (TBHP) as oxidant. By dissolving complex 2 in the room temperature ionic liquid 1-butyl-3-methylpyridinium tetrafluoroborate, the catalytic performance with TBHP was improved (higher selectivity to the aldehyde and higher Cy8 conversions). For Cy8 oxidation, the unreacted substrate and products were easily extracted with n-hexane, and the ionic phase containing the catalyst could be reused without loss of catalytic performance.     

Carbon-based nanostructured catalyst for biodiesel production by catalytic distillation

A promising carbon-based nanostructured catalyst was prepared via the following four steps: (1) thermal decomposition of organometallic compound (C₁₀H₁₄CoO₄) on 304 stainless steel substrate, (2) cracking of benzene to carbon nanotubes (CNTs) on the substrate using Co particle catalyst, (3) sulfurizing CNTs with Na₂S_x, and (4) oxidating the sulfurized CNTs with hydrogen peroxide. The as-prepared carbon-based catalyst was characterized by spectroscopy, scanning electron microscopy, transmission electron microscopy etc. The monolithic catalyst can serve as appropriate filler for a catalytic distillation column. Catalytic activity was examined by catalyzing the transesterification of soybean oil and methanol to biodiesel in the catalytic distillation column.     

Influence of the Ethylene Glycol, Water Treatment and Microwave Irradiation on the Characteristics and Performance of VPO Catalysts for n-Butane Oxidation to Maleic Anhydride

In this paper, the preparation of vanadium phosphate catalysts was shown to be improved by (1) using V₂O₅ and ethylene glycol as starting and reducing agent material, respectively for VOPO₄ · 2H₂O, (2) subsequent water treatment and (3) microwave irradiation. In particular, the preparation route, based on the reduction of VOPO₄ · 2H₂O with various alcohols, is described in detail and contrasted with other three established methods performed by using ethylene glycol and isobutyl alcohol as reductant and solvent for V₂O₅ or distilled water as a solvent material. The preparation of catalyst precursor is carried out by two different methods, namely conventional heating and microwave irradiation. With this new technique, catalysts derived from the reduction of VOPO₄ · 2H₂O by ethylene glycol exhibit substantially higher surface area (typically >40 m² g^?1) and activity. In fact, the surface area of the catalyst is significantly enhanced when the precursor is refluxed by distilled water and dried by microwave heating. The characterization of catalysts was carried out using X-ray diffraction (XRD), Brunauer–Emmer–Teller (BET) surface area measurement, temperature programmed reduction (H₂-TPR), temperature-programmed reaction (TPRn) and scanning electron microscopy (SEM). This study shows that employing ethylene glycol as reducing agent, followed by adding the water treatment step to catalyst synthesis procedure, and using microwave irradiation would give rise to enhanced surface area, activity and selectivity of the catalyst. Moreover, it introduces a more energy efficient procedure for preparation of vanadium phosphate catalyst used in selective oxidation of n-butane process.     

Low-temperature continuous wet oxidation of trichloroethylene over CoOx/TiO2 catalysts

TiO₂-supported metal oxides such as CoO_x, CuO_x, NiO_x and FeO_x have been used for catalytic wet oxidation of trichloroethylene (TCE) in a continuous flow type fixed-bed reactor system, and the most promising catalyst for this wet catalysis has been characterized using XPS and XRD techniques. All the supported catalysts gave relatively low conversions for the wet oxidation at 36 °C, except for 5 wt% CoO_x/TiO₂ which exhibited a steady-state conversion of 45% via a transient activity behavior up to 1 h on stream. XPS measurements yielded that a Co 2p_3/2 main peak at 779.8 eV appeared with the 5 wt% CoO_x/TiO₂ catalyst after the continuous wet TCE oxidation at 36 °C for ca. 6 h (spent catalyst) and this binding energy value was equal to that of Co₃O₄ among reference Co compounds used here, while the catalyst calcined at 570 °C (fresh catalyst) possessed a main peak at 781.3 eV, very similar to that for CoTiO_x species such as CoTiO₃ and Co₂TiO₄. Only characteristic reflections for Co₃O₄ were indicated upon XRD measurements even with the fresh catalyst sample. The simplest model, based on these XPS and XRD results, for nanosized Co₃O₄ particles existing with the fresh catalyst could reasonably explain the transient activity behavior observed upon the wet TCE oxidation.     

Oxidative Dehydrogenation of <Emphasis Type="Italic">n</Emphasis>-Butene to 1,3-Butadiene over Sulfated ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Catalyst

Oxidative dehydrogenation of n-butene to 1,3-butadiene over sulfated ZnFe₂O₄ catalyst was carried out in a continuous flow fixed-bed reactor. The effect of sulfation on the catalytic performance of ZnFe₂O₄ was investigated. Sulfated ZnFe₂O₄ catalyst showed a better catalytic performance than ZnFe₂O₄ catalyst in the oxidative dehydrogenation of n-butene. Acid–base property of sulfated ZnFe₂O₄ catalyst was measured by TPD experiment, with an aim of correlating the catalytic performance with the surface acid–base property of the catalyst. It was revealed that the catalytic performance of sulfated ZnFe₂O₄ catalyst was closely related to the surface weak-acid density of the catalyst. The enhanced acidity of sulfated ZnFe₂O₄ catalyst was responsible for its high catalytic performance in the oxidative dehydrogenation of n-butene. Thus, sulfation served as an efficient method for improving catalytic performance of ZnFe₂O₄ in the oxidative dehydrogenation of n-butene.     

Benzene hydroisomerization over Pt/MOR/Al2O3 catalysts

Benzene hydroisomerization is among the promising processes converting benzene into methylcyclopentane (MCP), which is an environmentally friendlier, octane boosting component of motor fuels. Benzene hydroisomerization into MCP over the Pt/MOR/Al₂O₃ (MOR = mordenite) catalytic system is reported here. The dependence of the yield of the target product on the acidic properties of the support and platinum precursor ([Pt(NH₃)₄]Cl₂ or H₂PtCl₆) have been investigated in order to optimize the catalyst composition. The acidic properties of the surface have been altered by introducing 30–95 wt % alumina into the support. Catalytic activity has been measured in the hydroisomerization of cyclohexane and a benzene (20 wt %) + n-heptane (80 wt %) mixture in a flow reactor at 250–350°C, 1.5 MPa, H₂: CH = 3: 1, a cyclohexane LHSV of 6 h^?1, a mixed feedstock LHSV of 2 h^?1, a catalyst bed volume of 2 cm³, and catalyst pellet sizes of 0.25–0.75 mm. The most efficient catalyst for cyclohexane and n-heptane isomerization and benzene hydroisomerization is the platinum-containing catalyst (0.3 wt % Pt) whose support consists of 30 wt % MOR and 70 wt % Al2O3. The highest yield of the target products of isomerization in the presence of this catalyst is attained in the temperature range from 280 to 310°C, which is thermodynamically favorable for MCP formation from benzene. This indicates that this catalyst is promising for the hydroisomerization of benzene-containing gasoline fractions. Use of H₂PtCl₆, a readily available chemical, as the platinum precursor is favorable for commercialization of the catalyst and ensures price attractiveness in its industrial-scale manufacturing.     

Polyoxometalate-catalysed epoxidation of propylene with hydrogen peroxide: microemulsion versus biphasic process

Epoxidation of propylene with H₂O₂ catalysed by peroxo polytungstophosphates (P:W = 1:4), prepared by interaction of H₂WO₄, H₂O₂ and H₃PO₄ in the presence of Aliquat 336 as a surfactant, has been studied in chloride-free water-in-oil microemulsion (ME) Brij 30^® – n-octane – 30% aqueous H₂O₂ in comparison with the epoxidation in biphasic system 1,2-dichloroethane – H₂O. The epoxidation in ME occurs readily at 40–80 °C to give propylene oxide with 89–97% selectivity together with 3–11% propylene glycol. The catalyst can be reused but with a significant loss of activity. ³¹P NMR and chemical analysis indicate that the polyoxometalate catalyst is unstable in the ME system. In contrast, the epoxidation in the biphasic system occurs without catalyst decomposition, giving 83–86% epoxide and 14–17% glycol, and the catalyst can be easily reused without loss of activity and selectivity. The H₂O₂ utilisation in biphasic system (97–100%) has been found to be higher than in ME system (70–85%) at 60 °C.     

Selective reduction of NOx with hydrocarbons over Co/MFI prepared by sublimation of CoBr2 and other methods

Co/MFI catalysts were prepared by various methods, including wet-ion exchange (WIE), either as such or in combination with impregnation (IMP), solid-state ion exchange (SSI), and sublimation (SUB) of CoCl₂ (at 700°C) or CoBr₂ (at 600°C) onto H/MFI. The catalysts were tested for the reduction of NO_x with CH₄ or iso-C₄H₁₀ in excess O₂. Below 425°C the SUB catalysts show the highest NO_x reduction activity with CH₄ or iso-C₄H₁₀. Above 425°C, the best performance is given by WIE. Below the temperature of maximum N₂ yield, a mixture of Fe/FER and WIE is superior to either catalyst. Addition of 10% H₂O to the feed drastically decreases the N₂ yield in NO_x reduction with CH₄, but increases the activity with iso-C₄H₁₀ under some conditions. Permanent damage of the zeolite lattice as a potential cause for the adverse effect of H₂O in the tests with CH₄ is eliminated, as the original activity is fully restored after calcination. A 100 h test with a wet iso-C₄H₁₀ feed shows excellent stability with a SUB catalyst prepared from CoBr₂.Characterization by XRD, H₂-TPR, and FTIR reveals that WIE contains isolated Co²⁺ and (Co–OH)⁺ ions that are only reducible at 700°C. SUB catalysts show additional TPR peaks at low temperature, including a feature at 220–250°C, ascribed to multinuclear Co oxo-ions. The formation of an NO_y chemisorption complex is most rapid on these catalysts. No oxidation states between Co⁰ and Co²⁺ are detectable; the one-step reduction of Co²⁺ to Co⁰ clusters could be a cause for the unique propensity of Co/MFI to reduce NO_x with CH₄.     

Synthesis of isoalkanes over Fe–Zn–Zr/HY composite catalyst through carbon dioxide hydrogenation

The reaction path of isoalkanes formation via CO₂ hydrogenation was studied over the Fe–Zn–Zr/HY composite catalyst, which gives high selectivity to isoalkanes. The results indicate that the reverse water–gas shift reaction is not the indispensable step for the synthesis of hydrocarbons. And i-C₄ (iso-butane) is formed from propylene and methanol through MTG (methanol to gasoline) reaction and i-C₅ (iso-pentane) obtained from the reaction of C₂ and C₃ through the additive dimerization. A part of C₁, C₄ is formed on the sole Fe–Zn–Zr catalyst from methanol for the CO₂ hydrogenation over Fe–Zn–Zr/HY composite catalyst.     

The promotion effects of Pd on Fe-Cu-Co based catalyst for higher alcohols synthesis

To increase the ability of Fe-Cu-Co based catalyst for hydrogen activation, the catalyst loaded with Pd was studied in the conversion of syngas to higher alcohols. X-ray diffraction (XRD), N₂ physisorption, H₂ temperature-programmed reduction (TPR) and H₂ temperature-programmed desorption (H₂-TPD) were applied to characterize the catalysts. The results of XRD showed that the Pd-loaded Fe-Cu-Co based samples were mainly composed of CuFe₂O₄ and CuO. After reduction, metallic Cu and Fe along with minor CuFe₂O₄ were identified, and the amount of CuFe₂O₄ decreased with the increase of the Pd content. H₂-TPR revealed that Pd facilitated the reduction of Fe-Cu-Co based catalyst. H₂-TPD confirmed that Pd enhanced the ability of Fe-Cu-Co based catalyst for H₂ activation. Therefore, the activity of the catalyst and the selectivity of alcohols were greatly improved. Over the Fe-Cu-Co based catalyst loaded with 0.5 wt.% Pd, the selectivity and the time-space yield of alcohols reached 58.7% and 1.53 g mL^− 1 h^− 1 at 350 °C, 6.0 MPa, GHSV = 10,000 h^− 1 and n(H₂)/n(CO) = 2.4.     

La-promoted Ni/γ-Al2O3 catalyst for autothermal reforming of methane

Autothermal reforming (ATR) of methane over the synthesized catalysts of 10Ni-2La/γ-Al₂O₃, 10Ni-2Ce/γ-Al₂O₃, 10Ni-2Co/γ-Al₂O₃ was investigated in the temperature range of 600-800 oC for the hydrogen production. The sequence of 2 wt% metal loading on nickel alumina support in relation to their catalytic performance was observed as La>Ce>Co. The excellent activity and selectivity of 10Ni-2La/γ-Al₂O₃ was superior to other catalysts owing to little carbon deposition (~2.23 mg coke/gcath), high surface area and good dispersion and stability in the alumina support. The reforming of methane was inferred to be initiated by the decomposition of hydrocarbon at the inlet zone, preceded by the reforming reactions in the catalyst bed. Our result shows that it can be possible to achieve the H₂/CO ratio optimal to the GTL processes by controlling the O₂/CH₄ ratio of the feed inlet. The addition of oxygen to the feed inlet enhanced conversion efficiency substantially; probably, it favors the re-oxidation of carbonaceous residues formed over the catalyst surfaces, avoiding the catalyst deactivation and hence promoting catalyst stability.     

Fe3O4 nanoparticles impregnated eggshell as a novel catalyst for enhanced biodiesel production

Biodiesel is a green fuel which can replace diesel while addressing various issues such as scarcity of hydrocarbon fuels and environmental pollution to an extent. The high production cost of biodiesel and the recovery of the catalyst after the transesterification process are the major challenges to be addressed in biodiesel production. In the present work, a cheap and promising solid base oxide catalyst was synthesized from chicken eggshell by calcination at 900 °C forming catalyst eggshells (CES) and was impregnated with the nanomagnetic material (Fe₃O₄) to obtain Fe₃O₄ loaded catalytic eggshell (CES–Fe₃O₄). Fe₃O₄ nanomaterials were synthesized by co-precipitation method and were loaded in catalytic eggshell by sonication, for better recovery of the catalyst after transesterification process. CES–Fe₃O₄ material was characterized by Thermogravimetric analysis, X-ray diffraction, Fourier transform infrared spectroscopy, a vibrating-sample magnetometer, Brunauer-Emmett-Teller, Dynamic light scattering, and Scanning electron microscopy. Biodiesel was synthesized by transesterification of Pongamia pinnata raw oil with 1:12 oil to methanol molar ratio and 2 wt% catalyst loading for 2 h at a temperature of 65 °C and yields were compared. The reusability of the catalyst was studied by the transesterification of the raw oil and its catalytic activity was found to be retained up to 7 cycles with a yield of 98%.     

Large-scale production of high-quality multi-walled carbon nanotubes: Role of precursor gas and of Fe-catalyst support

The crucial role of precursor gas (PG) and of catalyst support (CS) in the growth of multi-walled C nanotubes (MWCNTs) by iron-catalysed chemical vapour deposition (CVD) is evidenced. This is accomplished by comparing structural and morphological properties of MWCNTs synthesised by the use of different PGs (ethane and isobutane) and CSs (silica and alumina). The results of analyses, carried out on catalysts and C deposits by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS), thermo-gravimetry (TG) and X-ray diffraction (XRD), demonstrate that Al₂O₃-supported catalysts are more efficient than SiO₂-supported ones in decomposing hydrocarbons. The use of i-C₄H₁₀ as PG allows reducing Fe-encapsulation and improving yield (Y_C) and selectivity, so as the large-scale production (Y_C > 900 wt.%) of high-quality nanotubes can be operated even at moderate reaction temperature (600 °C) after proper calibration of Fe-load (29 wt.%) and catalyst reduction temperature (500 °C).     

Reduction behaviors and catalytic properties for methanol steam reforming of Cu-based spinel compounds CuX2O4 (X=Fe,Mn, Al,La)

In this study, various Cu-based spinel compounds, i.e., CuFe₂O₄, CuMn₂O₄, CuAl₂O₄ and CuLa₂O₄, were fabricated by a solid-state reaction method. Reduction behaviors and morphological changes of these materials have been characterized by H₂ temperature-programmed reduction (H₂-TPR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Moreover, the catalytic properties for steam reforming of methanol (SRM) of these Cu-based spinel compounds were investigated. H₂-TPR results indicated that the reducibility of Cu-based spinel compounds was strongly dependent on the B-site component while the CuFe₂O₄ catalyst revealed the lowest reduction temperature (190 °C), followed respectively by CuAl₂O₄ (267 °C), CuMn₂O₄ (270 °C), and CuLa₂O₄ (326 °C). The reduced CuAl₂O₄ catalyst demonstrated the best performance in terms of catalytic activity. Based on the SEM and XRD results, pulverization of the CuAl₂O₄ particles due to gas evolution and a high concentration of nanosized Cu particles (≈50.9 nm) precipitated on the surfaces of the Al₂O₃ support were observed after reduction at 360 °C in H₂. The BET surface area of the CuAl₂O₄ catalyst escalated from 5.5 to 13.2 m²/g. Reduction of Cu-based spinel ferrites appear to be a potential synthesis route for preparing a catalyst with high catalytic activity and thermal stability. The catalytic performance of these copper-oxide composites was superior to those of conventional copper catalysts.